1. Field of the Invention
The invention relates to the field of the manufacture of composite structural members and, in particular, to a process for making hollow tubular structural members and the like having integral attachment end fittings.
2. Description of Related Art
With the advent of light-weight, high-strength composite materials having organic matrix materials, there has been a trend to replace many metal structural members on aircraft with such materials. However, the typical methods of joining metals, such as welding, riveting and bolting are not necessarily efficient methods for composite materials. In fact, simply replacing the metal components of a complex structure with components made of composite materials may not produce a weight or cost savings. Such reductions will only occur when due recognition is given to the fact that composite materials depend primarily on the filamentary reinforcements in the resin matrix for their high strength and modulus to weight ratios.
For example, in hollow tubular members such as struts, control rods, or support beams made from metal most often the end fitting is joined to the end of the hollow member by bolts or rivets. In many control rods the end of the tube is swagged over an attachment end fitting. In the former method the composite material may not have the bearing strength to absorb the highly localized stress loads. In the latter, swagging will severely damage the filamentary material. Additionally, the resin matrix material will not take the highly localized deformation without cracking. Of course, if the resin matrix material is a thermoplastic material that only melts when heated to forming temperatures, the end of the fitting could be heated to a point wherein the resin is soft and malleable. However, as previously stated, the filamentary material may not withstand the swagging. If the matrix material were a thermoset resin, one that cures (under goes a chemical change) when heated to forming temperatures no subsequent forming can be accomplished thereafter.
With hollow tubular members using thermoplastic resin matrix materials, attempts have been made to form an integral attachment fitting during or after the forming of the hollow tubular member. However, the flattening of the end of the tube into a rectangular plate has, generally resulted in a non-uniform transition portion between it and the circular portion of the tube. In addition, without both internal and external pressure, the transition portion will not be properly consolidated. Furthermore, the thin tube wall, even when flattened, often will not provide the necessary bearing strength to absorb the localized loads induced by fasteners. Thus, what is required is a process for forming an integral attachment end fitting that provides the necessary fastener hole bearing strength and, additionally, a smooth and consolidated transition between the flattened plate portion and the circular tube.
Thus it is a primary object of the subject invention to provide a process of making hollow tubular structural members and the like having integral end attachment fittings.
It is another primary object of the subject invention to provide a process of making hollow tubular structural members and the like having integral end attachment fittings from composite structural materials.
It is a further object of the subject invention to provide a process of making hollow tubular structural members and the like having integral end attachment fittings from composite structural materials that incorporate thermoplastic resin matrix materials.